Electrospinning apparatus and electrospinning method

ABSTRACT

According to an embodiment, an electrospinning apparatus includes a head assembly and a pair of conductors. In the head assembly, a plurality of heads are arranged. Each head has a head main body, and nozzles projecting outward from the outer periphery surface of the head main body, and configured to eject a raw material liquid. The conductors are respectively arranged on the outer sides of the head assembly with respect to the head arrangement direction, and generate an electric field when a voltage of the same polarity as the voltage applied to the heads is applied. The cross-sectional area of each conductor in a cross section in the head-arrangement direction is smaller than the cross-sectional area of each head main body in a cross section in the head-arrangement direction.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2020-046100, filed Mar. 17, 2020; the entire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate to an electrospinning apparatus and an electrospinning method.

BACKGROUND

An electrospinning apparatus that accumulates microfibers on the surface of a conveyed substrate to form a fiber film with an electrospinning method (sometimes called “electric charge induction spinning method”) is known. In such an electrospinning apparatus, a plurality of heads are arranged in the direction of conveyance of the substrate. Each of the electrospinning heads includes a head main body and a plurality of nozzles projecting from the outer peripheral surface of the head main body. An ejection port for a raw material liquid is provided at the projecting end of the each nozzle projecting from the head main body. A voltage is applied between each nozzle and a collection body or a substrate so as to cause the nozzle to eject a raw material liquid from the ejection port against the surface of the collection body or the substrate, thereby accumulating fiber thereon.

With the above-described electrospinning apparatus, there is a demand to make uniform an intensity of a generated electric field among the heads arranged in the direction of conveyance of the substrate for improving the quality of the fiber film.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing an example of an electrospinning apparatus according to an embodiment.

FIG. 2 is a block diagram showing an example of a control configuration of the electrospinning apparatus according to the embodiment.

FIG. 3 is a perspective view schematically showing one of a plurality of heads according to the embodiment.

FIG. 4 is a cross-sectional view schematically showing one of a plurality of heads according to the embodiment in a cross section parallel to or approximately parallel to a direction of conveyance of a substrate, and parallel to or approximately parallel to the width direction of the substrate.

FIG. 5 is a cross-sectional view schematically showing the head assembly and the conductors according to the embodiment in a cross section parallel to or approximately parallel to the direction of conveyance of the substrate and perpendicular to or approximately perpendicular to the width direction of the substrate.

DETAILED DESCRIPTION

According to an embodiment, an electrospinning apparatus includes a head assembly and a pair of conductors. In the head assembly, a plurality of heads are arranged. Each head has a head main body provided with a storage hollow for storing a raw material liquid, and nozzles made of an electrically conductive material and projecting outward from the outer periphery surface of the head main body, and configured to eject the raw material liquid upon application of a voltage to the nozzles. The conductors, made of an electrically conductive material, are respectively arranged on the outer sides of the head assembly with respect to the head arrangement direction, and generate an electric field when a voltage of the same polarity as the voltage applied to the heads is applied. The cross-sectional area of each conductor in a cross section in the head-arrangement direction is smaller than the cross-sectional area of each head main body in a cross section in the head-arrangement direction.

According to the embodiment, the electrospinning method includes: preparing a head assembly in which a plurality of heads are arranged, each head having a head main body provided with a storage hollow for storing a raw material liquid, and nozzles projecting from the other peripheral surface of the head main body and having electrically conductive properties; applying a voltage to the raw material liquid stored in the storage hollow to cause each of the nozzles to eject the raw material liquid; and applying a voltage of the same polarity as the voltage applied to the raw material liquid to a conductor having a cross-sectional area smaller than the cross-sectional area of each head main body in a cross section in the head-arrangement direction.

Hereinafter, the embodiment will be described in detail with reference to the accompanying drawings.

Embodiment

FIG. 1 is a diagram showing a configuration of an electrospinning apparatus 10 according to the embodiment. FIG. 2 is a block diagram showing a control configuration of the electrospinning apparatus 10 according to the embodiment. The electrospinning apparatus 10 is an apparatus that forms a fiber film on a substrate 40 by an electrospinning method (sometimes called “electric charge induction spinning method”). The substrate 40 is a sheet-shaped electrode, for example. The substrate 40 is made of a material having resistance to a raw material liquid. The substrate 40 is made of aluminum, for example.

As shown in FIGS. 1 and 2, the electrospinning apparatus 10 includes a housing 13, an electric power supply 20, a head assembly 30, an unwinding reel 41, a winding reel 42, a support body 50, a conveyance device 60, and a control device 80. The electric power supply 20 is electrically connected to the head assembly 30. The electric power supply 20 supplies power to the head assembly 30 so as to electrically charge a raw material liquid supplied to the head assembly 30.

The head assembly 30, the support body 50, and the conveyance device 60 are arranged inside the housing 13. The support body 50 is placed inside the housing 13, and supports the head assembly 30.

The unwinding reel 41 and the winding reel 42 are arranged outside the housing 13, and are rotated by a driving source (not shown). The housing 13 has an inlet 11 and an outlet 12. At each of the inlet 11 and the outlet 12, the inside of the housing 13 communicates with the outside of the housing 13. The unwinding reel 41 supplies the substrate 40 to the conveyance device 60 in the housing 13, via the inlet 11. The conveyance device 60 conveys the substrate 40 supplied from the unwinding reel 41. The head assembly 30 ejects the electrically charged raw material liquid against the substrate 40 conveyed by the conveyance device 60, and forms a fiber film on the substrate 40. The substrate 40 on which the fiber film is formed is conveyed to the outside of the housing 13 through the outlet 12, and is collected by the winding reel 42.

The conveyance device 60 includes four rollers 61, a horizontal conveyance path 63, and two vertical conveyance paths 64. Each of the vertical conveyance paths 64 extends in the vertical direction (the Y1 direction or the Y2 direction in FIG. 1). The horizontal conveyance path 63 extends in the horizontal direction (the X direction in FIG. 1). The rollers 61 are arranged at the upper end of each of the vertical conveyance paths 64, and at a boundary between each of the vertical conveyance paths 64 and the horizontal conveyance path 63. The substrate 40 is supported at each roller 61, and the vertical conveyance paths 64 and the horizontal conveyance path 63 are thereby constituted. The rollers 61 are rotated by the driving source 62 having a motor. By the rotation of the rollers 61, the substrate 40 is conveyed on the conveyance path of the substrate 40, including the horizontal conveyance path 63 and the vertical conveyance paths 64. Herein, in the situation where the conveyance device 60 conveys the substrate 40, the direction perpendicular to the extending direction of the horizontal conveyance path 63 (the X direction in FIG. 1) and the direction perpendicular to the vertical direction (the Y1 and Y2 directions in FIG. 1) correspond to or approximately correspond to the width direction of the substrate 40. The number of vertical conveyance paths, the number of horizontal conveyance paths, and the number of rollers are not limited to those given in the present embodiment.

At a position facing one of the vertical conveyance paths 64, either one of the two head assemblies 30 is arranged. Each of the head assemblies 30 is connected to a raw material liquid storage tank (a supply source of a raw material liquid) (not shown) via a liquid transmitting mechanism (not shown). To each of the head assemblies 30, a liquid material is supplied from the liquid material storage tank. Each of the head assemblies 30 is electrically connected to the power supply 20. To each of the head assemblies 30, a voltage is applied by the power supply 20. Each head assembly 30 ejects the electrically charged raw material liquid against one side of the substrate 40 conveyed by the vertical conveyance path 64 that the head faces. The solvent in the raw material liquid ejected from the head assembly 30 volatilizes in an atmosphere in the electrospinning apparatus 10. The ingredients of the raw material liquid ejected from the head assembly 30 shoot out, and reach one side of the substrate 40 conveyed in the vertical conveyance path 64. The accumulation of the ingredients that have reached the substrate 40 forms a fiber film on the substrate 40.

The raw material liquid for the fiber is a solution in which the ingredients of the fiber dissolve in a solvent at a predetermined concentration.

The ingredients of the fiber may be changed as appropriate in accordance with a material of a fiber film desired to be formed. Examples of the ingredients for the fiber are: a polyolefin-type resin, a thermoplastic resin, and thermoset resin. Specifically, examples of the thermoplastic resin that can be the ingredients for the fiber are: polystyrene, polycarbonate, polymethyl methacrylate, polypropylene, polyethylene, polyethylene terephthalate, polybutylene terephthalate, polyamide, polyoxymethylene, polyamide-imide, polyimide, polysulfone, polyethersulfone, polyetherimide, polyetherketon, polyphenylenesulfide, modified-polyphenyleneether, syndiotactic polystyrene, and liquid crystal polymer. Examples of the thermoset resin that can be the ingredients for the fiber are: urea resin, unsaturated polyester resin, phenol resin, melamine resin, and epoxy resin. A copolymer that contains the aforementioned resins may be used as the ingredients for the fiber. The ingredients of the fiber may be made by mix-spinning of one, two, or more types of polymers selected from the above-listed resins and a copolymer. The ingredients of the fiber applicable to the present embodiment is not limited to the above-listed substances. The listed ingredients of the fiber are merely examples.

Any solvent can be used as long as the ingredients of the fiber can dissolve into the solvent. The solvent may be changed as appropriate in accordance with the ingredients of the fiber to be dissolved. As the solvent, an alcohol-type solvent, a volatile organic solvent such as aromatic series, or water may be used. Examples of the organic solvent are: isopropanol, ethylene glycol, cyclohexanone, dimethylformamide, acetone, ethyl acetate, dimethylacetamide, N-methylpyrrolidinone, hexane, toluene, xylene, methyl ethyl ketone, diethyl ketone, butyl acetate, tetrahydrofuran, dioxiane, pyridine, etc. The solvent may be one type selected from the above-listed solvents, or a mixture of a few types. The solvent applicable to the present embodiment is not limited to the above-listed solvents. The listed solvents are merely examples.

The space between the head assembly 30 and the vertical conveyance path 64 is determined by ejection conditions, for example, a voltage applied to the head assembly 30, a type of the polymer in the raw material liquid, a concentration of the ingredients of the fiber contained in the raw material liquid, etc.

The substrate 40 is interposed between the roller 61 arranged at the upper end of the vertical conveyance path 64 and the head assembly 30. On the other hand, no substrate 40 is interposed between the roller 61 arranged at the connecting part where the horizontal conveyance path 63 is connected to the vertical conveyance path 64 and the head assembly 30. For this reason, the roller 61 arranged at the connecting part where the horizontal conveyance path 63 is connected to the vertical conveyance path 64 faces the head assembly 30 without the substrate 40 interposed therebetween.

To improve the speed of forming the fiber film, the head assembly may be arranged at both sides of each vertical conveyance path 64, and the fiber film may be formed on both surfaces of the substrate 40.

Next, the configuration of the head assembly 30 is described. Each head assembly 30 has five heads 31A through 31E. The heads 31A through 31E have the same structure. The head assembly 30 may be called a “head group”.

The heads 31A through 31E are supported by the support body 50 in a state of facing the vertical conveyance path 64. The heads 31A through 31E are arranged in the vertical direction. In other words, the heads 31A through 31E are arranged in the direction of conveyance of the substrate 40 along the vertical conveyance path 64 to which the heads are opposed. Each of the heads 31A through 31E extends in the width direction of the substrate 40. The head 31A is located the highest among the heads 31A through 31E. The head 31E is located the lowest among the heads 31A through 31E. The heads 31B through 31D are located between the heads 31A and 31E with respect to the vertical direction. The heads 31A through 31E are arranged at equal intervals with respect to the vertical direction.

Next, the configuration of the heads 31A through 31E is described. The structure of the head 31A will be explained as an example with reference to FIGS. 3 through 5. The explanations of the heads 31B through 31E are omitted as they have the same structure as the head 31A. FIG. 3 is a perspective view schematically showing the head 31A. FIG. 4 is a cross-sectional view schematically showing the head 31A in a cross section parallel to or approximately parallel to the direction of conveyance of the substrate 40, and parallel to or approximately parallel to the width direction of the substrate 40. FIG. 4 shows the head 31A in a cross section parallel to or approximately parallel to a center axis C, which will be described later. FIG. 5 is a cross-sectional view schematically showing the head assembly 30, etc. in a cross section parallel to or approximately parallel to the direction of conveyance of the substrate 40 and perpendicular to or approximately perpendicular to the width direction of the substrate 40. FIG. 5 shows the heads 31A through 31E in a cross section perpendicular to or approximately perpendicular to the center axis C, which will be described later.

As shown in FIGS. 3 through 5, the head 31A has a head main body 311 and eight nozzles 312A through 312H. The head main body 311 and each of the nozzles 312A through 312H are made of a material having electric conductivity (an electrically conductive material). Preferably, the head main body 311 and each of the nozzles 312A through 312H are made of a material having resistance against a raw material liquid, and may be made of stainless steel, for example.

The head main body 311 has a center axis C, and extends along the center axis C. The center axis C is an axis parallel to or approximately parallel to the width direction of the substrate 40. In the present embodiment, the outer shape of the head main body 311 in a cross section perpendicular to or approximately perpendicular to the center axis C is formed in the shape of a roughly regular hexagon. The outer peripheral surface of the head main body 311 extends around the center axis C, and constitutes a part of the outer surface of the head main body 311. Furthermore, the outer peripheral surface of the head main body 311 is directed to the side away from the center axis C with respect to the direction intersecting (perpendicular or substantially perpendicular to) the center axis C.

Inside the head main body 311, a storage hollow 315 is formed along the center axis C. In the storage hollow 315, a raw material liquid supplied from the liquid transmitting mechanism (not shown) is accumulated. The head main body 311 is formed into a cylindrical shape having the storage hollow 315 as an internal hollow. The storage hollow 315 is formed over the entirety or the majority of the head main body 311 in the direction of the center axis C. In the present embodiment, the storage hollow 315 is formed in an approximately round shape in a cross section perpendicular to or approximately perpendicular to the center axis C.

Each of the nozzles 312A through 312H is provided on the outer peripheral surface of the head main body 311. The nozzles 312A through 312H are arranged on the side where the vertical conveyance path 64 is located, with respect to the center axis C. Each of the nozzles 312A through 312H projects outwardly from the outer peripheral surface of the head main body 311 toward the opposed-to vertical conveyance path 64. The nozzles 312A-312H are arranged separately from each other with respect to the direction along with the center axis C, and are arranged in a zig-zag manner. Of the nozzles 312A through 312H, the nozzles 312A and 312H are located at the ends in the direction of the center axis C.

On the inside of each of the nozzles 312A through 312H, a flow passage communicating with the storage hollow 315 is formed. In each of the nozzles 312A through 312H, one ejection port is formed at the end on the outer peripheral side. One end of the flow passage of each of the nozzles 312A through 312H communicates with the storage hollow 315, and each flow passage extends from the storage hollow 315 toward the outer periphery side of the head main body 311. The other end of the flow passage opens externally at the ejection port. In other words, in each of the nozzles 312A through 312H, the ejection port of the flow passage is formed at the projecting end of the corresponding nozzle on the outer peripheral surface of the head main body 311.

The nozzles 312A through 312H constitute two nozzle lines 313A and 313B arranged at different positions around the center axis C of the head main body 311 (the peripheral direction of the outer periphery of the head main body 311). The nozzle line 313A consists of the nozzles 312A through 312D. The nozzles 312A through 312D are arranged at the same or substantially the same angle positions around the center axis C. In the nozzle line 313A, the nozzles 312A and 312D are located at the ends of the nozzle line in the direction of the center axis C. The nozzle line 313B consists of the nozzles 312E through 312H. The nozzles 312E through 312H are arranged at the same or substantially the same angle positions, which differ from those at which the nozzles 312A through 312D are arranged, around the center axis C. For example, the nozzles 312A through 312D are arranged about 60 degrees deviated from the nozzles 312E through 312H around the center axis C. In the nozzle line 313B, the nozzles 312E and 312H are located at the ends of the nozzle line in the direction of the center axis C. The nozzle line 313A is a first nozzle line. The nozzle line 313B is a second nozzle line. Each of the nozzle lines 313A and 313B may be called a “nozzle group”.

In the outer peripheral surface of the head main body 311, the nozzles constituting the nozzle line 313A and the nozzles constituting the nozzle line 313B are alternately arranged, with respect to the direction of the center axis C. For example, the nozzle 312E constituting the nozzle line 313B is arranged between the nozzles 312A and 312B constituting the nozzle line 313A. Since the nozzle line 313A and the nozzle line 313B are arranged at different positions around the center axis C, the nozzles 312A through 312H are arranged in a zig-zag manner on the outer peripheral surface of the head main body 311. With this configuration, it is possible to prevent local accumulation of the raw material liquid ejected onto the substrate 40.

The power supply 20 applies a voltage between the head 31A and the substrate 40. To each of the nozzles 312A through 312H, a voltage of a predetermined polarity is applied by the power supply 20 via the head main body 311. The nozzles 312A through 312H are electrically connected to each other. For this reason, when a voltage is applied to the nozzles 312A through 312H, they are at the same or substantially the same potential. The polarity of the voltage applied to each of the nozzles 312A through 312H may be positive or negative. The power supply 20 is a direct current power supply for example, and applies a positive voltage to each of the nozzles 312A through 312H.

The substrate 40 is grounded. In the situation where a positive voltage is applied to each of the nozzles 312A through 312H, the ground voltage of the substrate 40 becomes 0 V or substantially 0 V. The substrate 40 is not necessarily grounded. In this case, the power supply 20 applies to the substrate 40 a voltage of a polarity opposite to that of the voltage applied to the nozzles 312A through 312H.

In the situation where the head 31A is supplied with the raw material liquid, the voltage is also applied to the raw material liquid when the voltage is applied between each of the nozzles 312A through 312H and the substrate 40 by the power supply 20, and the raw material liquid is ejected against the substrate 40 from the ejection port of each of the nozzles 312A through 312H. In other words, the potential difference between each of the nozzles 312A through 312H and the substrate 40 causes the ejection of the raw material liquid to which the voltage has been applied against the substrate 40. Through the ejection of the liquid material against the substrate 40 from the ejection port of each of the nozzles 312A through 312H, the raw material liquid partially accumulates on the surface of the substrate 40, and the accumulated raw material liquid forms a fiber film. Thus, the fiber film is formed by the electrospinning method (sometimes referred to as an “electric charge induction spinning method”).

The voltage applied between the head 31A and the substrate 40, namely the potential difference between each of the nozzles 312A through 312H and the substrate 40, is adjusted to be of an appropriate value in accordance with the type of the high polymer included in the raw material liquid and a distance between each of the nozzles 312A through 312H and the substrate 40, and the like. In one example, a direct current voltage in the range from 10 kV to 100 kV is applied between each of the nozzles 312A through 312H and the substrate 40.

Any structure can be adopted as the power supply 20 as long as it applies a voltage to each of the nozzles 312A through 312H. For example, a voltage may be applied to each of the nozzles 312A through 312H without involving the head main body 311. In this case, a terminal electrically connected to the power supply 20 is provided in each of the nozzles 312A through 312H. A voltage is applied to each of the nozzles 312A through 312H via this terminal. With this configuration, the head main body 311 may be made of a non-conductive material.

The number of heads included in the head assembly 30 is not limited to five. For example, the number of heads provided in the head assembly 30 may be two to four, or six or more. The number of nozzles provided in a single head is not limited to a particular number. At least one nozzle should be provided in each head.

As an example where a fiber film is formed on the surface of the substrate 40, manufacturing of a separator-integrated type electrode for a battery is known. In this example, either one of the negative electrode or the positive electrode of an electrode group may be used as the substrate. The fiber film formed on the surface of the substrate 40 serves as a separator integrated with the negative electrode or the positive electrode.

The control device (controller) 80 is a computer, for example. The control device 80 has a processor or an integrated circuit (control circuit) including a CPU (central processing unit), an ASIC (application specific integrated circuit), or an FPGA (field programmable gate array), and a storage medium, such as a memory. The control device 80 may include only one integrated circuit, etc., or a plurality of integrated circuits, etc. The control device 80 performs processing by executing a program, etc. stored on the storage medium, etc. The control device 80 controls the driving of the above-described driving sources (for example, the driving source 62), the operation of the liquid transmitting mechanism, the output of the power supply 20, etc.

As shown in FIG. 1, a pair of conductors 70A and 70B is attached to the head assembly 30. The conductors 70A and 70B are supported by being attached to the support body 50. Each of the conductors 70A and 70B may be called a “controlling body” or an “electric field controlling stick”.

The conductor 70A is attached above the heads 31A through 31E of the head assembly 30. The conductor 70B is attached below the heads 31A through 31E of the head assembly 30. Thus, the conductors 70A and 70B are arranged on the outer sides of the head assembly 30 respectively, with respect to the vertical direction. In other words, one of the conductors 70A and 70B is arranged next to one end of the head assembly 30 in the direction of conveyance of the substrate 40, and the other of the conductors 70A and 70B is arranged next to the other end.

The conductors 70A and 70B are made of a material having electric conductivity (a conductive material) such as a metal, etc. It is preferable that the conductors 70A and 70B be made of the same material as the nozzles 312A through 312H of the head assembly 30.

The conductors 70A and 70B extend in the direction parallel to or approximately parallel to the extending direction of the heads 31A through 31E of the head assembly 30 (for example, the center axis C). In other words, the conductors 70A and 70B extend in the width direction of the substrate 40. In the present embodiment, the conductors 70A and 70B are stick-shaped members extending in the width direction of the substrate 40. The conductors 70A and 70B may be, for example, plate-shaped members extending in the width direction of the substrate 40.

The length of each of the conductors 70A and 70B in the extending direction may be the same as the length of the head main body 311 in the extending direction (the width direction of the substrate 40), or shorter than the length of the head main body 311 in the extending direction (the width direction of the substrate 40), for example. The length of each of the conductors 70A and 70B in the extending direction (the width direction of the substrate 40) may be longer than the length of the head main body 311 in the extending direction (the width direction of the substrate 40) in order to control the shooting path of the raw material liquid.

Each of the conductors 70A and 70B is electrically connected to the power supply 20. The power supply 20 applies a voltage to each of the conductors 70A and 70B. To each of the conductors 70A and 70B, a voltage of the same polarity as the voltage applied to each nozzle of the head assembly 30 is applied by the power supply 20. For example, to each of the conductors 70A and 70B, a voltage of the same value as the voltage applied to the head assembly 30 is applied. The voltage applied to the conductors 70A and 70B may be smaller than the voltage applied to the head assembly 30, or may be larger than the voltage applied to the head assembly 30 in order to control the shooting path of the fiber.

In the present embodiment, the power supply 20 supplies power to both of the head assembly 30 and the conductors 70A and 70B. To apply different voltages to the conductors 70A and 70B and the head assembly 30, the power supply that supplies power to the head assembly 30 and the power supply that supplies power to the conductors 70A and 70B may be separately provided.

FIG. 5 shows the position relationship of the conductors 70A and 70B and the head assembly 30. FIG. 5 shows a cross section parallel to or approximately parallel to the direction of conveyance of the substrate 40 and perpendicular or approximately perpendicular to the width direction of the substrate 40 (the center axis C of the head main body 311 and the center axes of the conductors 70A and 70B).

As shown in FIG. 5, the head-to-head pitch d1 of the heads 31A through 31E is a value in the range of 150 mm to 350 mm. The head-to-head pitch d1 is a distance between the two adjacent heads among the heads 31A through 31E in the direction of arrangement of the heads 31A through 31E, for example a distance between the head 31A and the head 31B in the direction of arrangement of the heads 31A through 31E.

The distance d2 from one end of the array of the heads 31A through 31E to the conductor 70A or 70B in the direction of arrangement of the heads 31A through 31E is shorter than the head-to-head pitch d1. In other words, the distance from the head closest to the conductor among the plurality of heads and the conductor in the direction of arrangement of the heads 31A through 31E is shorter than the head-to-head distance in the direction of arrangement of the heads 31A through 31E. For example, the distance d2 between the conductor 70A and the head 31A and the distance d2 between the conductor 70B and the head 31E are shorter than the head-to-head pitch d1.

In a cross section in the arrangement direction of the heads 31A through 31E, namely a cross section perpendicular to or approximately perpendicular to the center axis C, the diameter d5 of each of the conductors 70A and 70B is smaller than the length d3 of the diagonal line of the head main body 311. For this reason, the cross-sectional area of each of the conductors 70A and 70B in a cross section perpendicular to or approximately perpendicular to the center axis C is smaller than the cross-sectional area of the head main body 311 including the storage hollow 315 in a cross section perpendicular to or approximately perpendicular to the center axis C. In other words, the cross-sectional area of the part surrounded by the outer peripheral surface of each of the conductors 70A and 70B in a cross section in the arrangement direction of the heads 31A through 31E is smaller than the cross-sectional area of the part surrounded by the outer peripheral surface of the head main body 311 in a cross section in the arrangement direction of the heads 31A through 31E.

In a cross section perpendicular to or approximately perpendicular to the center axis C, the diameter d5 of the conductors 70A and 70B is larger than the diameter d4 of the storage hollow 315.

Thus, in the present embodiment, the diameter of the conductors 70A and 70B is larger than the diameter of the storage hollow 315, and smaller than the outer diameter of the head main body 311. The diameter of the conductors 70A and 70B may be smaller than the diameter of the storage hollow 315.

Next, operations and advantageous effects of the electrospinning apparatus 10 according to the present embodiment will be described.

When forming a fiber film on the substrate 40 conveyed on the vertical conveyance path 64, first, electric power is supplied to each of the heads 31A through 31E from the power supply 20 while the raw material liquid is being supplied to the heads 31A through 31E. In each of the heads 31A through 31E, a predetermined voltage is applied between each of the nozzles 312A through 312H and the substrate 40. In each of the heads 31A through 31E, an electric field is generated in the vicinity of the ejection ports of the nozzles 312A through 312H when a voltage is applied to the nozzles 312A through 312H. At this time, the electric fields in the vicinity of the heads 31A through 31E are influenced by the electric field generated in the nozzles arranged near the electric fields.

For example, an electric field in the vicinity of the heads 31B through 31D located between the heads 31A and 31E on the ends in the arrangement direction of the heads 31A through 31E (vertical direction) is influenced by the electric fields generated in two adjacent heads on both sides (for example, two of the heads 31A through 31E) with respect to the arrangement direction of the heads 31A through 31E. For example, the nozzle 312A of the head 31B does not deviate with respect to the nozzle 312A of the head 31A and the nozzle 312A of the head 31C in the extending direction (the direction of the center axis C). Furthermore, the nozzle 312A of the head 31B is adjacent to each of the nozzle 312A of the head 31A and the nozzle 312A of the head 31C with respect to the arrangement direction of the heads 31A through 31E. For these reasons, the electric field in the vicinity of the nozzle 312A of the head 31B is influenced by the electric field generated in the nozzle 312A of the head 31A and the electric field generated in the nozzle 312A of the head 31C.

On the other hand, an electric field in the vicinity of the head 31A or 31E located at the end of the arrangement direction of the heads 31A through 31E is influenced by an electric field generated in an adjacent head on one side of the head 31A (or 31E) (for example, the head 31B or the head 31D) with respect to the arrangement direction of the heads 31A through 31E. For example, the nozzle 312F of the head 31E does not deviate with respect to the nozzle 312F of the head 31D in the extending direction (the direction of the center axis C). Furthermore, the nozzle 312F of the head 31E is adjacent to the nozzle 312F of the head 31D in the arrangement direction of the heads 31A through 31E. For these reasons, the electric field in the vicinity of the nozzle 312F of the head 31E is influenced by the electric field generated in the nozzle 312F of the head 31D.

For this reason, there is a possibility that the electric field intensity may vary between the heads arranged at the ends of the head assembly 30 (for example, the heads 31A and 31E) and the heads arranged at the center of the head assembly 30 (for example, the heads 31B through 31D), due to the difference in the number of adjacent heads.

In the present embodiment, the conductors 70A and 70B are arranged on the outer sides of the heads 31A through 31E in the arrangement direction of the heads 31A through 31E, and a voltage of the same polarity as the voltage applied to each of the heads 31A through 31E is applied to the conductors 70A and 70B. In the vicinity of each of the conductors 70A and 70B, an electric field is generated upon application of a voltage to the conductor. For this reason, an electric field in the vicinity of a head arranged at either end of the head assembly 30 (e.g., the head 31A or 31E) is influenced by an electric field generated in a conductor adjacent to the head (either the conductor 70A or 70B), in addition to the influence of the electric field generated in the head adjacent to the head located at the end in the arrangement direction of the heads 31A through 31E (e.g., the head 31B or 31D). For this reason, a difference in the electric field intensity between the heads arranged at the ends of the head assembly 30 (for example, the heads 31A and 31E) and the heads arranged at the center of the head assembly 30 (for example, the heads 31B through 31D) can be suppressed. When the variations in the electric field intensity between the heads 31A through 31E in the head assembly 30 are suppressed, the shooting out of the raw material liquid, which depends on the potential difference between the head assembly 30 and the substrate 40, becomes uniform, and the fiber film formed on the substrate 40 can be uniformly formed. This effect effectively works particularly on a configuration where three or more heads are arranged in the head assembly 30.

The fiber ejected from the head assembly 30 shoots out toward the substrate 40 conveyed on the vertical conveyance path 64, and also shoots out in a direction other than the direction toward the substrate 40 in the vertical direction. In the present embodiment, because of an electric field generated in the vicinity of the conductors 70A and 70B, the vertical-direction expansion of the shooting path of the fiber ejected from each of the nozzles 312A through 312H of each of the heads 31A through 31E can be suppressed. For this reason, for example, the shooting of the fiber toward the rollers 61 located below the vertical conveyance path 64 can be suppressed, and the shooting of the fiber toward a wall surface located above the vertical conveyance path 64 (for example, ceiling) can be prevented. Accordingly, with the conductors 70A and 70B provided, the adhesion of the fiber to the rollers 61 and the adhesion of the fiber to the wall surfaces can be suppressed, and it is thereby possible to accurately control an amount of the raw material liquid to be ejected. For this reason, it is possible to suppress unevenness in the fiber film thickness formed on the substrate 40, and to reduce the loss of the raw material liquid.

Furthermore, the diameter d5 of each of the conductors 70A and 70B is smaller than the length d3 of the diagonal line of the head main body 311 in the cross section vertical to or approximately vertical to the center axis C. In other words, the outer diameter of each of the conductors 70A and 70B is smaller than the outer diameter of the head main body 311. For this reason, if the same voltage is applied to each of the heads 31A through 31E and the conductors 70A and 70B, it is possible to make the distance d2 from either the head 31A or 31E on the end of the head assembly 30 to the conductor 70A or 70B smaller than the head-to-head pitch d1. If the respective distances d2 from the heads 31A and 31E on the ends of the head assembly 30 to the conductors 70A and 70B are made smaller, the length of the part including the conductors 70A and 70B and the head assembly 30 in the direction of conveyance of the substrate 40 can be made smaller. It is thereby possible to suppress variations in the electric field intensity between the heads 31A through 31E of the head assembly 30, and to realize downsizing of a device.

In the present embodiment, in each of the heads 31A through 31E of the head assembly 30, two nozzle lines 313A and 313B are alternately arranged in a direction of the center axis C. In this case, it may be possible that variations in electric field intensity in the vicinity of nozzles may be caused due to a difference in electric fields generated in the vicinity, between the nozzle arranged on one end of the nozzle line 313A and the nozzle arranged on the same-side end of the nozzle line 313B. For example, in the vicinity of the nozzle 312E arranged on one end of the nozzle line 313B, three nozzles (312F, 312A, and 312B) are arranged. On the other hand, in the vicinity of the nozzle 312A arranged on one end of the nozzle line 313A, two nozzles (312B and 312E) are arranged. For this reason, due to the difference in the number of nozzles arranged nearby, variations in electric field intensity in the vicinity of the nozzles arranged on the same-side ends may be caused between the nozzle line 313A and the nozzle line 313B. As described above, in the present embodiment, with the conductors 70A and 70B provided, variations in electric field intensity among the heads 31A through 31E can be suppressed. Through the suppression of the variations in electric field intensity among the heads 31A through 31E, variations in electric field intensity in the vicinity of the nozzles arranged on a same-side end of the same head (for example, the nozzles 312A and 312E of the head 31A) can also be suppressed.

In the present embodiment, a conductor is arranged in each of the ends of the head assembly 30 with respect to the direction of conveyance of the substrate 40; however, a conductor may be arranged on one end of the head assembly 30 with respect to the direction of conveyance of the substrate 40.

According to at least one of the foregoing embodiment or examples, the electrospinning apparatus has a conductor arranged at the end of the head assembly configured to generate electric fields when a voltage is applied thereon. It is thereby possible to provide an electrospinning apparatus that improves quality of a fiber film.

While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions. 

What is claimed is:
 1. An electrospinning apparatus comprising: a head assembly in which a plurality of heads are arranged, each head having a head main body in which a storage hollow for storing a raw material liquids is formed, and nozzles made of a conductive material and projecting outward from the outer periphery surface of the head main body, and configured to eject the raw material liquid upon application of a voltage to the nozzles; a pair of conductors arranged on each of the outer sides of the head assembly with respect to a direction of arrangement of the heads and made of a conductive material, the conductors configured to generate an electric field when a voltage of a same polarity as the voltage applied to the heads is applied, wherein a cross-sectional area of each of the conductors in a cross-section along a direction of arrangement of the heads is smaller than a cross-sectional area of each head main body in a cross-section along the direction of arrangement of the heads.
 2. The electrospinning apparatus according to claim 1, wherein a distance from a head closest to the conductor among the plurality of heads to the conductor in the direction of arrangement of the heads is shorter than a head-to-head distance in the direction of arrangement of the heads.
 3. The electrospinning apparatus according to claim 1, wherein each of the heads has a first nozzle line that includes a plurality of the nozzles arranged along a direction of a center axis of the head main body, and a second nozzle line that includes a plurality of the nozzles arranged along the center axis of the head main body, the second nozzle being arranged at a location different from a location of the first nozzle line around the center axis of the head main body, and the nozzles that constitute the first nozzle line and the nozzles that constitute the second nozzle line are alternately arranged with respect to the direction of the center axis of the head main body.
 4. The electrospinning apparatus according to claim 1, wherein in each of the heads, the nozzle projects from the head main body toward a substrate and ejects the raw material liquid toward the substrate, a center axis of the head main body intersects a direction of conveyance of the substrate, and the plurality of heads are arranged in the direction of conveyance of the substrate.
 5. The electrospinning apparatus according to claim 4, wherein the head assembly is provided facing a conveyance path that conveys the substrate in a vertical direction, and the plurality of heads are arranged in a vertical direction.
 6. An electrospinning method, comprising: preparing a head assembly in which a plurality of heads are arranged, each head having a head main body in which a storage hollow for storing a raw material liquid is formed, and nozzles having an electrical conductivity and projecting outward from an outer peripheral surface of the head main body; applying a voltage to the raw material liquid stored in the storage hollow to cause the nozzle to eject the raw material liquid; and applying a voltage of a same polarity as a voltage applied to the raw material liquid to a pair of conductors, the conductors being arranged at outer ends of the head assembly in a direction of arrangement of the heads and each having a cross-sectional area smaller than a cross-sectional area of each head main body in the direction of arrangement of the heads. 